JP2009042497A - Surface plasmon element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface plasmon element having a sharp surface plasmon resonance peak and excellent wavelength selectivity. <P>SOLUTION: The surface plasmon element has an electric conductive film 20 formed on a substrate 10, on which electric conductive film 20 openings 21 are periodically arranged and the intensity of light passing through the openings 21 is intensified by the periodical arrangement, further a periodical structure of refractive index distribution is provided in the transmission direction of the light in the opening 21 through which the light passes. The periodic structure of the refractive index distribution is formed by the periodical variation of the refractive index of a dielectric bodies 30 filled in the openings 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an element having a surface plasmon effect, and more particularly to a surface plasmon element capable of obtaining a sharp surface plasmon resonance peak.

  Patent Document 1 discloses a technique for significantly improving the transmittance of light transmitted through an aperture row by using a metal thin film provided with an aperture row (aperture array) having a diameter equal to or smaller than the wavelength of light. According to Patent Document 1, by arranging the openings in a periodic arrangement, light that is incident on the metal thin film passes through one or more openings having a diameter equal to or less than a wavelength provided in the metal thin film. Is significantly enhanced compared to the absence of a periodic aperture, and such enhancement occurs when light incident on the metal film interacts resonantly with a surface plasmon mode excited by the metal film. It is described.

  In addition to a structure in which circular openings are periodically arranged in a metal thin film, Patent Document 1 proposes a parallel slit (slit array) structure in which slits are arranged in parallel. There is described a method of amplifying transmitted light transmitted through an opening by providing a periodic ring-shaped groove around a circular opening of one wavelength or less. Furthermore, in Patent Document 3, in order to increase the utilization efficiency of the transmitted light obtained with respect to incident light, the opening diameter on the first surface side through which light enters the opening is made larger than the opening diameter on the second surface side. Are listed.

On the other hand, several proposals have been made regarding the use of such a surface plasmon enhancement effect. Patent Document 1 describes application to a wavelength selection filter, a mask for photolithography, and the like, and Patent Document 2 describes application to a read / write head for an optical storage medium. Patent Document 4 describes application to a small surface plasmon resonance sensor.
Japanese Patent No. 3008931 JP 2001-291265 A JP 2004-288240 A JP 2005-308658 A

  By the way, when applying the surface plasmon enhancement effect to, for example, a wavelength selection filter, the sharpness of the selected wavelength (the narrowness of the half width) is required. Also, in the case of sensor applications, it is effective to sharpen the surface plasmon resonance peak where surface plasmon enhancement occurs for higher sensitivity. This means that when a very small amount of material is attached to the sensor, even if the surface plasmon resonance peak wavelength shifts slightly, if the peak is sharp, the intensity change becomes very large, and sensing of a very small amount of material is possible. Because it becomes. Furthermore, with regard to the application to read / write heads for optical storage media, multiple recording becomes easier as the surface plasmon resonance peak at which surface plasmon enhancement occurs is sharper in order to support a recording method using a plurality of wavelengths. This is a very important characteristic for increasing the density.

  However, the surface plasmon resonance peak is prominent in the conventional structure in which the openings below the wavelength are periodically provided in the metal film or the structure in which the ring-shaped grooves are periodically provided around the single opening below the wavelength. However, there has been little study on the optimum structure for sharpening.

  The present invention has been made in view of such circumstances, and provides a high-performance surface plasmon element that does not require a large-scale optical system and can obtain a sharp surface plasmon resonance peak as compared with the prior art. For the purpose.

  According to the invention of claim 1, in the surface plasmon element in which the conductive film is formed on the substrate, the openings are periodically arranged in the conductive film, and the intensity of light transmitted through the openings is enhanced by the periodic arrangement. A periodic structure having a refractive index distribution is provided in the light transmission direction in the opening through which light passes.

  According to the second aspect of the present invention, the conductive film is formed on the substrate, and the conductive film is provided with at least one opening and a periodic array of recesses or through-holes. In a surface plasmon element that enhances the intensity, a periodic structure having a refractive index distribution is provided in the light transmission direction in an opening through which light is transmitted.

  In the invention of claim 3, in the invention of claim 1 or 2, the periodic structure of the refractive index distribution is constituted by a periodic change of the refractive index of the dielectric filled in the opening.

  In the invention of claim 4, in the invention of claim 1 or 2, the periodic structure of the refractive index profile is constituted by a periodic change in the shape of the side wall of the opening.

  According to this invention, a surface plasmon element having a sharp surface plasmon resonance peak and excellent wavelength selectivity can be obtained. Therefore, it is possible to improve the performance of the surface plasmon element, and it is possible to contribute to improving the performance of various sensors and optical communication devices that use the surface plasmon element.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an outline of the configuration of a first embodiment of a surface plasmon element according to the present invention. In this example, the surface plasmon element includes a substrate 10, a conductive film 20 formed on the substrate 10, and its conductivity. A dielectric 30 filled in an opening 21 provided in a periodic arrangement on the film 20 is formed.

  In this example, the openings 21 are slits arranged in parallel at a predetermined pitch, and are provided through the conductive film 20 in the thickness direction. Due to the periodic arrangement of the openings 21, the intensity of light transmitted through the openings 21 is enhanced by the surface plasmon effect.

  Although the detailed illustration of the dielectric 30 filled in the opening 21 is omitted in FIG. 1, it is a dielectric multilayer film in which a high refractive index layer and a low refractive index layer are alternately laminated. In this example, a periodic structure of a refractive index distribution is provided in the opening 21 in the light transmission direction due to the periodic change of the refractive index due to the layer and the low refractive index layer. In FIG. 1, an arrow A indicates a light transmission direction.

  FIG. 2 schematically shows a manufacturing process of the surface plasmon element shown in FIG. 1. Hereinafter, the steps (1) to (5) will be described with reference to FIG. A typical configuration example will be described.

(1) A quartz substrate was prepared as the substrate 10, and Si was formed as a high refractive index layer and SiO ₂ was formed as a low refractive index layer by sputtering on the substrate 10 and laminated alternately. The thickness of the high refractive index layer H is 66.8 nm, the thickness of the low refractive index layer L is 150 nm, the high refractive index layer H and the low refractive index layer L are laminated three times / two times, and then the cavity is low. A refractive index layer was formed to a thickness of 300 nm, and then a high refractive index layer H and a low refractive index layer L were laminated three times / two times. In the figure, 2L indicates a cavity.

  (2) A resist was coated on the uppermost high refractive index layer H, and was exposed and developed to form a resist pattern 41. The resist pattern 41 was a line-and-space pattern with a pitch of 1 μm and a line width of 0.5 μm.

  (3) The high refractive index layer H and the low refractive index layer L were etched by ion beam etching using the resist pattern 41 as a mask.

  (4) The resist pattern 41 was removed, and the conductive film 20 was formed by sputtering. The conductive film 20 is a metal film, and Ag is used for the metal film in this example.

  (5) The surface of the surface plasmon element was manufactured by removing the excess conductive film 20 by planarizing and polishing the surface.

  FIG. 3A shows the result of measuring the transmitted light spectrum as the optical characteristics of the surface plasmon element manufactured as described above, and FIG. 3B shows the enlarged peak portion.

  It can be seen from FIGS. 3A and 3B that a very sharp transmitted light peak is obtained. As a result of measuring the sharpness of the transmitted light peak of this surface plasmon element, the performance is improved by about two orders of magnitude compared to the conventional surface plasmon element in which there is no periodic change in refractive index in the light transmission direction in the opening 21 of the conductive film 20. Was achieved.

  In this example, the periodic structure of the refractive index distribution in the light transmission direction in the openings 21 periodically arranged in the conductive film 20 is realized by periodically changing the shape of the side walls of the openings 21. Hereinafter, a manufacturing process and a specific configuration will be described with reference to FIGS.

  (1) A quartz substrate was prepared as the substrate 10, and Si was formed as the optically transparent layer 31 on the substrate 10 by sputtering. The thickness of the optical transparent layer 31 was 1.5 μm. Then, a resist was applied on the optical transparent layer 31 and exposed and developed to form a resist pattern 42.

(2) SiO ₂ was formed as a mask material by sputtering, and a SiO ₂ mask (mask pattern) 43 was formed by lift-off. The mask 43 was a line and space pattern, with a pitch of 1 μm and a line width of 0.5 μm. Then, the optically transparent layer 31 is etched by a so-called Bosch method (for example, described in JP-A-7-503815), in which etching and deposition are alternately performed, and the side wall of the etched hole is etched. A periodic structure with irregularities was formed. The period (pitch) P and the step D of the unevenness were approximately the following values.
P: 250 nm
D: 50 nm

  (3) After removing the mask 43, the conductive film 20 was formed by sputtering. The conductive film 20 was a metal film, and Ag was used.

  (4) The surface of the surface plasmon element was fabricated by removing the excess conductive film 20 by planarizing and polishing the surface. The openings 21 periodically arranged in the conductive film 20 have a periodic change in shape on the side wall thereof.

  FIG. 5 shows the result of measurement of the transmitted light spectrum as the optical characteristics of the surface plasmon element produced as described above, and it can be seen that a sharp transmitted light peak is obtained. As a result of measuring the sharpness of the transmitted light peak of this surface plasmon element, the performance is about three times that of a conventional surface plasmon element in which the side wall of the opening 21 of the conductive film 20 has no periodic change in shape in the light transmission direction. Improvements have been achieved.

[Comparative example]
A surface plasmon element was produced using the same method as in Example 1 except that a periodic structure in which high refractive index layers and low refractive index layers were alternately laminated was not formed. That is, the inside of the openings 21 periodically arranged in the conductive film 20 is configured by only a low refractive index layer.

  As an optical characteristic of the surface plasmon element, a transmitted light spectrum was measured. The results are shown in FIG. FIG. 6 shows that the transmitted light peak is very broad in this example.

  As described above, according to the present invention, the surface plasmon resonance peak can be made extremely sharp, and a high-performance surface plasmon element can be obtained in that respect.

  Such an effect is due to the three-dimensional structure control that introduces periodicity in the light transmission direction in the surface plasmon element, and the period of the refractive index distribution in the light transmission direction in the light transmission opening. It has been found for the first time in the present invention that wavelength selectivity is very effectively produced when a structure is introduced. Details of this mechanism are not clear, but there is a coupling between a two-dimensional periodic array structure that enhances the intensity of light transmitted through the aperture and a periodic structure of a refractive index distribution provided in the light transmission direction. It is guessed.

  In the above-described embodiments, Ag is used as the material of the conductive film 20, but not limited to Ag, for example, a material that has been known to cause surface plasmon resonance, such as Au, Al, Cr, can be used.

  In addition, the periodic arrangement structure causing the enhancement effect of transmitted light is not limited to a structure in which slits are arranged in parallel (line and space structure), for example, a structure or light in which circular openings through which light is transmitted are two-dimensionally arranged periodically. Various structures conventionally known, such as a structure in which grooves are periodically arranged concentrically around the opening through which light is transmitted, can be employed.

  FIGS. 7 and 8 show examples of such a periodic arrangement structure. FIG. 7 shows that the conductive film 20 is provided with circular openings 21 ′ having a diameter equal to or smaller than the wavelength of light arranged in a square lattice pattern. FIG. 8 shows an example in which circular recesses 22 are periodically arranged in a square lattice pattern around a single circular opening 21 ′. 7 and 8, the opening 21 'is filled with a dielectric 30 having a periodic change in refractive index, as in the first embodiment.

The perspective view which shows the structure outline | summary of the 1st Example of the surface plasmon element by this invention. The schematic diagram for demonstrating the manufacturing process of the surface plasmon element shown in FIG. A is a graph showing the transmitted light spectrum of the surface plasmon element shown in FIG. 1, and B is a graph in which the peak portion is enlarged. The schematic diagram for demonstrating the structure and manufacturing process of the 2nd Example of the surface plasmon element by this invention. The graph which shows the transmitted light spectrum of the surface plasmon element demonstrated in FIG. The graph which shows the transmitted light spectrum of the surface plasmon element of a comparative example (conventional structure). The top view which shows the 3rd Example of the surface plasmon element by this invention. The top view which shows the 4th Example of the surface plasmon element by this invention.

Claims (4)

In a surface plasmon element in which a conductive film is formed on a substrate, and openings are periodically arranged in the conductive film, and the intensity of light transmitted through the openings is increased by the periodic arrangement,
A surface plasmon element comprising a periodic structure having a refractive index distribution in a light transmitting direction in the opening through which light is transmitted. In a surface plasmon element in which a conductive film is formed on a substrate, and the conductive film is provided with at least one opening and a periodic array of recesses or through holes, and the intensity of light transmitted through the opening is enhanced by the periodic array,
A surface plasmon element comprising a periodic structure having a refractive index distribution in a light transmitting direction in the opening through which light is transmitted. In the surface plasmon element according to claim 1 or 2,
The surface plasmon element, wherein the periodic structure of the refractive index distribution is constituted by a periodic change in the refractive index of a dielectric filled in the opening. In the surface plasmon element according to claim 1 or 2,
The surface plasmon element characterized in that the periodic structure of the refractive index distribution is constituted by a periodic change in the shape of the side wall of the opening.